1. Field of the Invention
The present invention relates to exposure apparatus, substrate processing systems, and device manufacturing methods, and more particularly to an exposure apparatus used in a lithographic process when manufacturing devices such as a semiconductor device, a liquid crystal display device, a plasma display device, or a thin film magnetic head, a substrate processing system having the exposure apparatus and a substrate processor connected inline to the exposure apparatus, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
In conventional lithographic process for manufacturing devices such as semiconductors, various exposure apparatus have been used. In recent years, the ones mainly used are projection exposure apparatus that move in a step-by-step fashion, such as a reduction projection exposure apparatus based on a step-and-repeat method, that is, the so-called stepper, or a scanning projection exposure apparatus based on a step-and-scan method, that is, the so-called scanning stepper.
While the degree of integration increases in semiconductor devices, the device rule (practical minimum, line width) is decreasing, and in order to comply with such a situation, exposure apparatus require high exposure accuracy. In addition, since these types of exposure apparatus are used for mass-production of devices, high throughput is naturally required, in addition to exposure accuracy.
Exposure accuracy has been improved, conventionally, by measures such as increasing the number of numerical apertures (N.A.) in a projection optical system to improve the resolution, and improving the positional controllability of a wafer stage (in the case of a stepper) or a wafer stage and a reticle stage (in the case of a scanning stepper). Furthermore, throughput has been improved, mainly by increasing the speed of above stages or the like.
Recently, however, the degree of integration in semiconductor devices is increasing intensely, and with such situation exposure apparatus are also facing further requirements for improvement in their performance. It is, however, becoming difficult to achieve the recent tight requirements by the conventional methods referred to above or by similar methods. That is, the numerical aperture of the projection optical system cannot be increased too much, since it leads to narrowing the depth of focus. In addition, exposure wavelength has become shorter, and exposure apparatus using an ArF excimer laser having a wavelength of 193 nm as its light source has entered the stage of practical usage. However, new problems have occurred with such wavelength or light having a shorter wavelength; that they are greatly absorbed by air (oxygen), water vapor, hydrogen carbonate gas, or the like.
In addition, increasing the speed of the wafer stage or the reticle stage may cause the throughput or exposure accuracy to reduce. That is, increasing the speed of these stages leads to an increase in settling time for position setting, or an increase in synchronous settling time of both stages on scanning exposure. In addition, increasing the speed also increases vibration, which may aggravate the positional controllability of the stages.
Under such circumstances, a proposal of an exposure apparatus of a double stage type, which comprises two wafer stages, has recently been made in order to achieve improvement in throughput from a different perspective. With such an apparatus, an almost continuous exposure is possible by exposing a wafer on one wafer stage while performing wafer exchange or alignment on the other wafer stage, and then continuing the above operations with the stages switched. Thus, throughput is considered to increase drastically, with such an apparatus.
With the double wafer stage type exposure apparatus, however, the reaction force caused by the movement of the wafer stage where operations such as alignment is performed may be the cause of vibration in the other wafer stage where exposure is performed. This may lead to a decrease in exposure accuracy, which may reduce the yield of the end products, or the devices. Accordingly, from an overall perspective, productivity of the devices may not always be improved.
In addition, even if the double wafer stage method is employed, the problem of the transmittance of the exposure light decreasing due to absorption of the exposure light referred to earlier still remains. Also, if the double wafer stages are simply employed, the footprint will increase due to larger stage supporting beds. This will restrict the number of exposure apparatus units that can be arranged in a clean room in a semiconductor factory. Since the running cost of a clean room is extremely expensive, as a whole, the productivity of the devices may not always be improved.